FLUCTUATION EFFECTS ON THE ELECTRODYNAMICS OF QUASI-ONE-DIMENSIONAL CONDUCTORS ABOVE THE CHARGE-DENSITY-WAVE TRANSITION

The complex conductivity spectra of the quasi-one-dimensional compounds K0.3MoO3 (blue bronze) and (TaSe4)(2)I in the conducting phase (above T-3D = 183 K and 263 K, respectively, but below the mean-field temperature T-MF) have been measured over a broad frequency range, 1-10(5) cm(-1), using a combination of different spectroscopic techniques; we have also investigated the effects of disorder. Clearly pronounced excitations are discovered in the spectra below 50 cm(-1) for the electric field (E) over right arrow parallel to the chains, the direction along which the charge-density wave develops below the Peierls transition temperature T-3D. We associate these excitations with charge-density-wave fluctuations that exist even at room temperature and result in a collective contribution to the conductivity. For the transverse polarization, (E) over right arrow perpendicular to the chains, no such low-frequency excitations are evident in the conductivity spectra. These measurements give clear evidence for important deviations from conventional metallic behavior in the fluctuating region below T-MF but above T-3D, the temperature where three-dimensional long-range order develops.